xfs: delay initial open of the GC zone

The code currently used to select the new GC target zone when the
previous one is full also handles the case where there is no current GC
target zone at all.  Make use of that to simplify the logic in
xfs_zone_gc_mount.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hans Holmberg <hans.holmberg@wdc.com>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Carlos Maiolino <cmaiolino@redhat.com>
Signed-off-by: Carlos Maiolino <cem@kernel.org>

Author: Christoph Hellwig

fs/xfs/xfs_zone_gc.c

@@ -527,7 +527,7 @@ xfs_zone_gc_select_victim(
 	return true;
 }
 
-static struct xfs_open_zone *
+static int
 xfs_zone_gc_steal_open(
 	struct xfs_zone_info	*zi)
 {
@@ -538,15 +538,18 @@ xfs_zone_gc_steal_open(
 		if (!found || oz->oz_allocated < found->oz_allocated)
 			found = oz;
 	}
-
-	if (found) {
-		found->oz_is_gc = true;
-		list_del_init(&found->oz_entry);
-		zi->zi_nr_open_zones--;
+	if (!found) {
+		spin_unlock(&zi->zi_open_zones_lock);
+		return -EIO;
 	}
 
+	trace_xfs_zone_gc_target_opened(found->oz_rtg);
+	found->oz_is_gc = true;
+	list_del_init(&found->oz_entry);
+	zi->zi_nr_open_zones--;
+	zi->zi_open_gc_zone = found;
 	spin_unlock(&zi->zi_open_zones_lock);
-	return found;
+	return 0;
 }
 
 static struct xfs_open_zone *
@@ -1194,31 +1197,24 @@ xfs_zone_gc_mount(
 {
 	struct xfs_zone_info	*zi = mp->m_zone_info;
 	struct xfs_zone_gc_data	*data;
-	struct xfs_open_zone	*oz;
 	int			error;
 
 	/*
-	 * If there are no free zones available for GC, pick the open zone with
+	 * If there are no free zones available for GC, or the number of open
+	 * zones has reached the open zone limit, pick the open zone with
 	 * the least used space to GC into.  This should only happen after an
-	 * unclean shutdown near ENOSPC while GC was ongoing.
-	 *
-	 * We also need to do this for the first gc zone allocation if we
-	 * unmounted while at the open limit.
+	 * unclean shutdown while GC was ongoing.  Otherwise a GC zone will
+	 * be selected from the free zone pool on demand.
 	 */
 	if (!xfs_group_marked(mp, XG_TYPE_RTG, XFS_RTG_FREE) ||
-	    zi->zi_nr_open_zones == mp->m_max_open_zones)
-		oz = xfs_zone_gc_steal_open(zi);
-	else
-		oz = xfs_open_zone(mp, WRITE_LIFE_NOT_SET, true);
-	if (!oz) {
-		xfs_warn(mp, "unable to allocate a zone for gc");
-		error = -EIO;
-		goto out;
+	    zi->zi_nr_open_zones >= mp->m_max_open_zones) {
+		error = xfs_zone_gc_steal_open(zi);
+		if (error) {
+			xfs_warn(mp, "unable to steal an open zone for gc");
+			return error;
+		}
 	}
 
-	trace_xfs_zone_gc_target_opened(oz->oz_rtg);
-	zi->zi_open_gc_zone = oz;
-
 	data = xfs_zone_gc_data_alloc(mp);
 	if (!data) {
 		error = -ENOMEM;
@@ -1241,7 +1237,6 @@ xfs_zone_gc_mount(
 	kfree(data);
 out_put_gc_zone:
 	xfs_open_zone_put(zi->zi_open_gc_zone);
-out:
 	return error;
 }